Field of the Invention
The present invention relates to a heterocyclic compound and an organic light-emitting device including the heterocyclic compound.
Description of the Related Art
Organic light-emitting devices (OLEDs), which are self-emitting devices, have advantages such as wide viewing angles, excellent contrast, quick response, high brightness and excellent driving voltage characteristics, and they can provide multicolored images.
A typical OLED has a structure including a substrate and an anode, a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and a cathode, which are sequentially stacked on the substrate. In this regard, the HTL, the EML, and the ETL are organic thin films formed of organic compounds.
An operating principle of an OLED having the above-described structure is as follows.
When a voltage is applied between the anode and the cathode, holes injected from the anode move to the EML via the HTL, and electrons injected from the cathode move to the EML via the ETL. The holes and electrons recombine in the EML to generate excitons. When the excitons drop from an excited state to a ground state, light is emitted.
A major factor that affects luminescent efficiency of an OLED is the type of luminescent material used. Although fluorescent materials have been widely used as luminescent materials so far, development of a phosphorescent material able to improve luminescent efficiency up to four times based on theoretical electroluminescence mechanisms is an effective method for luminescent efficiency improvement. Iridium (III) complex-based phosphorescent materials have been widely known so far, and bis(2-(2′-benzothienyl)-pyridinato-N,C3′)iridium(acetylacetonate)) ((acac)Ir(btp)2), tris(2-phenylpyridine)iridium (Ir(ppy)3), and bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium (Firpic) are available for red, green and blue emission, respectively.

4, 4′-N,N′-dicarbazole-biphenyl (CBP) is the most widely known phosphorescent host material so far. A high-efficiency organic light-emitting device with a hole blocking layer formed from 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) or bis(2-methyl-8-quinolinato-N1,O8)-(1,1′-biphenyl-4-olato)aluminum (BAlq), and a high-performance OLED (Pioneer, Japan) using a BAlq derivative as a host are disclosed.

Although they have advantageous light-emitting characteristics, these existing luminescent materials have low glass transition temperatures and poor thermal stability, and thus they may be deteriorated during a high-temperature deposition process under vacuum. The power efficiency of an OLED may be represented as: Power efficiency=(π/Voltage)×Current Efficiency. That is, power efficiency is inversely proportional to voltage, and the power efficiency of the OLED should be high in order to achieve reduced power consumption. In practice, an OLED using a common phosphorescent (host) material such as BAlq or CBP may have a considerably higher current efficiency (cd/A) but also have a higher driving voltage, as compared with an OLED using a fluorescent material, and thus this arrangement is not advantageous in terms of power efficiency (lm/w). OLEDs using such a host material from the existing art are also not satisfactory in terms of lifetime. Therefore, there is a demand for development of a more stable host material with improved characteristics, allowing for both good current efficiency and good power efficiency.